Optical coherence tomography device

ABSTRACT

An optical coherence tomography device provided with: an OCT optical system configured to output OCT signal; and an analysis processing unit configured to process the OCT signal and generate motion contrast data of the specimen. The analysis processing unit is provided with: a first image data generation unit configured to process multiple OCT signals to generate first image data representing phase difference information of the multiple OCT signals, and a second image data generation unit configured to process the OCT signal to generate second image data representing amplitude information of the OCT signal. The analysis processing unit generates the motion contrast data based on the phase difference information in the first image data and the amplitude information in the second image data.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/566,778, filed Dec. 11, 2014, which claims priority from JapanesePatent Application No. 2013-258410, filed on Dec. 13, 2013, the contentsof all of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates an optical coherence tomography devicethat obtains motion contrast data of a specimen.

BACKGROUND

In the related art, as a device which performs angiography, for example,a fundus camera, a scanning laser optometry device, or the like has beenknown. In using this type of devices, a contrast agent which emits lightwith specific excitation light is injected into a body of a specimen.The device receives light from the contrast agent to obtain anangiographic image. That is, in the related art, the injection of thecontrast agent is required.

In recent years, a device which obtains motion contrast by applying anoptical coherence tomography (OCT) technique without using a contrastagent has been suggested as described in the following related-artdocuments.

Patent Document 1:

-   International Patent Publication No. 2010/143601    Non-Patent Document 1:-   Yonghua Zhao et al. OPTICS LETTERS/Vol. 25, No. 2/Jan. 15, 2000    Non-Patent Document 2:-   Adrian Mariampillai et al. OPTICS LETTERS/Vol. 33, No. 13/Jul. 1,    2008    Non-Patent Document 3-   Vivek J. Srinivasan et al. OPTICS LETTERS/Vol. 35, No. 1/Jan. 1,    2010

However, it is considered that a technique for obtaining a functionalOCT image, such as motion contrast, using OCT is still developing andstands further improvement.

SUMMARY OF THE INVENTION

The present disclosure has been made in view of the above circumstances,and one of objects of the present disclosure is to provide an opticalcoherence tomography device capable of acquiring a satisfactoryfunctional OCT image in consideration of the above-described problems.

According to an illustrative embodiment of the present disclosure, thereis provided an optical coherence tomography device that is providedwith: an OCT optical system configured to detect measurement lightirradiated onto a specimen and a reference light and output OCT signalbased on the measurement light and the reference light; and an analysisprocessing unit configured to process the OCT signal and generate motioncontrast data of the specimen. The analysis processing unit is providedwith: a first image data generation unit configured to process multipleOCT signals which is a plurality of OCT signals output from the OCToptical system being obtained at a different timing for the sameposition on the specimen and to generate first image data representingphase difference information of the multiple OCT signals; and a secondimage data generation unit configured to process the OCT signal outputfrom the OCT optical system to generate second image data representingamplitude information of the OCT signal. The analysis processing unit isconfigured to generate the motion contrast data based on the phasedifference information in the first image data generated by the firstimage data generation unit and the amplitude information in the secondimage data generated by the second image data generation unit.

According to another illustrative embodiment of the present disclosure,there is provided an optical coherence tomography device that isprovided with: an OCT optical system configured to detect measurementlight irradiated onto a specimen and a reference light and output OCTsignal based on the measurement light and the reference light; and ananalysis processing unit configured to process the OCT signal andgenerate functional OCT data of the specimen. The analysis processingunit is provided with: a first image data generation unit configured togenerate first functional OCT image data by applying first analysisprocessing on the OCT signal; and a second image data generation unitconfigured to generate at least one of OCT image data or secondfunctional OCT image data by applying second analysis processing that isdifferent from the first analysis processing on the OCT signal. Theanalysis processing unit is configured to generate the functional OCTimage data based on the first functional OCT image data generated by thefirst image data generation unit and at least one of the OCT image dataand the second functional OCT image data generated by the second imagedata generation unit.

According to another illustrative embodiment of the present disclosure,there is provided a method for controlling an optical coherencetomography device being provided with an OCT optical system configuredto detect measurement light irradiated onto a specimen and a referencelight and output OCT signal based on the measurement light and thereference light. The method includes: processing multiple OCT signalswhich is a plurality of OCT signals output from the OCT optical systembeing obtained at a different timing for the same position on thespecimen and to generate first image data representing phase differenceinformation of the multiple OCT signals; processing the OCT signaloutput from the OCT optical system to generate second image datarepresenting amplitude information of the OCT signal; and generating themotion contrast data based on the phase difference information in thefirst image data and the amplitude information in the second image data.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram illustrating a configuration of an opticalcoherence tomography device;

FIG. 2 is a diagram showing an outline of an optical system;

FIGS. 3A and 3B are image diagrams of a fundus oculi illustrating ameasurement according to an example;

FIG. 4 is a flowchart illustrating processing according to the example;

FIGS. 5A and 5B are diagrams illustrating image deviation;

FIG. 6 is a diagram showing a mode in which a phase difference of anon-vascular part is different for each A-Line;

FIG. 7 is a diagram illustrating a phase difference;

FIG. 8 is a diagram illustrating a denoising method;

FIG. 9 is a diagram illustrating a vector difference;

FIG. 10 is a diagram showing an image obtained by a Doppler phasemethod;

FIG. 11 is a diagram showing an image obtained by a vector differencemethod;

FIG. 12 is a diagram showing an image obtained by a vector differencemethod using a Doppler filter; and

FIG. 13 is a diagram showing an en-face image obtained by a vectordifference method using a Doppler filter.

DETAILED DESCRIPTION

Hereinafter, an overview of an illustrative embodiment according to thepresent invention will be described.

<Composition of Functional OCT Image>

An optical coherence tomography device 1 is provided with an OCT opticalsystem (OCT interferometer) 100 and an analysis processing unit (forexample, a control unit 70).

The OCT optical system 100 may be configured to detect measurement lightirradiated onto a specimen and a reference light and output OCT signalbased on the measurement light and the reference light.

The analysis processing unit may be configured to process the OCT signalto generate functional OCT image data in the specimen. The analysisprocessing unit may be provided with a first OCT image data generationunit and a second OCT image data generation unit. For example, the firstOCT image data generation unit may be configured to generate firstfunctional OCT image data by first analysis processing on the OCTsignal. For example, the second OCT image data generation unit may beconfigured to generate OCT image data or second functional OCT imagedata by second analysis processing different from the first analysisprocessing on the OCT signal.

For example, the analysis processing unit may be configured to generatea new functional OCT image based on first functional OCT image data andsecond functional OCT image data. With this, for example, it may bepossible to obtain functional OCT image data with high contrast andremoved unnecessary reflective components compared to individualfunctional OCT image data.

Functional OCT image data may be, for example, image data based on aDoppler OCT image (phase difference image) of Phase Difference, Phasevariance, Doppler variance, or the like, image data based on a vectordifference (VD) of a complex OCT signal, image data based onDecorrelation of an intensity signal, image data representing variationin intensity, such as Spectral variance, in the form of an image, or thelike. For example, functional OCT image data may be acquired byprocessing various OCT signals acquired from Scattering OCT,Polarization Sensitive OCT, Stereoscopic OCT, or the like. FunctionalOCT image data may be image data or signal data.

The functional OCT image data may be complex image data such as imagedata containing real part and imaginary part of the complex OCT signal.

For example, when the analysis processing unit generates a newfunctional OCT image based on first functional OCT image data and secondfunctional OCT image data, functional OCT image data acquired bydifferent analysis methods may be used as first functional OCT imagedata and second functional OCT image data. For example, image data basedon a Doppler OCT image may be used as first functional OCT image data,and image data based on a polarization sensitive OCT image may be usedas second functional OCT image data. For example, image data based on aScattering OCT image may be used as first functional OCT image data, andimage data based on a Stereoscopic OCT image may be used as secondfunctional OCT image data.

Various combinations are used as a combination of first functional OCTimage data and second functional OCT image data generated by differenttypes of analysis processing.

The analysis processing unit may be configured to generate a newfunctional OCT image based on first functional OCT image data and OCTimage data. As OCT image data, for example, image data representing themagnitude of the amplitude of the OCT signal in the form of an image,image data representing the intensity (a value obtained by squaring themagnitude of the amplitude) of the OCT signal, or the like may be used.

<Generation of Motion Contrast>

The optical coherence tomography device 1 may be configured to calculatemotion contrast of a sample by two or more methods from at least twotemporally different detection signals at the same position as afunctional OCT image. A combination of the results based on motioncontrast may be set as a sample image.

As a method of calculating motion contrast of the sample from theacquired complex OCT signal, for example, there is a method using aphase difference (PD) of a complex OCT signal (e.g. see Non-PatentDocument 1 for details; hereinafter, referred to as a Doppler phasemethod or a PD method), a method using a vector difference (VD) of acomplex OCT signal (e.g. see Non-Patent Document 3 for details;hereinafter, referred to as a vector difference method or a VD method),a method using spectral variance (SV) (e.g. see Non-Patent Document 2for details; hereinafter, referred to as a SV method), or the like.

The PD method calculates fluctuation in phase of a complex OCT signal,that is, a phase difference to calculate motion contrast of a sample.For example, the phase difference is calculated by Expression (3), whichis described later.

For example, an advantage of the PD method is that a signal with highreflection in a nerve fiber layer (NFL) or a retinal pigment epithelium(RPE) with no variation in phase is hardly detected because only a phasedifference is viewed. A disadvantage of the PD method may be that anartifact (a signal undesired to be detected) is detected by theinfluence of a blood vessel in a part in contact with the shadow of theblood vessel (see FIG. 10).

In the VD method, fluctuation in complex vector of a complex OCT signal,that is, a vector difference is calculated to calculate motion contrastof a sample. For example, the vector difference is calculated byExpression (5). For example, the amplitude of a complex OCT signal mayhave an influence on fluctuation in complex vector.

For example, an advantage of the VD method is that a signal of a bloodvessel becomes large and contrast is satisfactory because both amplitudeand phase are used. A disadvantage of the VD method may be that a signalin a high reflection part, such as an NFL, becomes large.

In the SV method, fluctuation in intensity of a complex OCT signal, thatis, variation of intensity is calculated to calculate motion contrast ofa sample.

A disadvantage of the SV method may be that an artifact is detected in ahigh reflection part because only intensity is viewed.

In this example, it is possible to skillfully use different advantagesof the respective computation methods by combining motion contrast ofthe sample computed by two or more methods described above.

For example, using two methods of the PD method and the VD method, thecontrol unit 70 detects a signal which has fluctuation in phase andfluctuation in complex vector. Since a vascular part has largefluctuation in phase and large fluctuation in complex vector, thecontrol unit 70 can skillfully detect a signal from the vascular part.

Doppler optical coherence tomography (referred to as DOCT) is means forobtaining a rate of a blood flow or the like on the condition that theamount of temporal change in phase (change in frequency) obtained byFourier transform of spectrum interference information corresponds tomoving speed of a subject as a Doppler signal (see Patent Document 1).In OCT, wavelength scanning OCT (time domain OCT), Fourier domain OCT,or the like can be applied.

For example, Doppler OCT is means for irradiating a predetermined regionof a specimen with measurement light twice at the time Δt so as tomeasure a blood flow rate of the predetermined region of the specimen,obtaining the amount Δϕ of temporal change in phase (hereinafter, simplyreferred to as an amount of change in phase or a phase difference) fromthe thus-obtained two tomographic images, calculating the amount oftemporal change in frequency (hereinafter, referred to as a frequencyshift) from the amount Δϕ of change in phase, and calculating andobtaining a blood flow rate of the region from an optical Dopplereffect.

Doppler OCT has tomographic image information at different times andphase information included in the tomographic image information for thesame region of the specimen. Meanwhile, according to the effect ofoptical Doppler, a frequency shift (change in frequency) of reflectedlight irradiated onto a mobile object corresponds to the speed of theobject.

<Analysis Processing Unit>

The analysis processing unit (for example, the control unit 70) may beconfigured to process an OCT signal to generate motion contrast data ina specimen. Motion contrast is, for example, detection information ofmotion of the specimen, temporal change, or the like. For example, aflow image or the like is a kind of motion contrast. For example, theflow image detection represents motion of a fluid or the like in theform of an image. An angiographic image which images a blood vesselposition obtained by detecting motion of blood is regarded as a kind ofmotion contrast. For example, the first image data generation unit mayprocess a plurality of temporally different OCT signals with respect tothe same position on the specimen. For example, the optical coherencetomography device 1 scans measurement light at least twice at the sameposition on the specimen to acquire temporally different OCT signals atthe same position. It is preferable that the first image data generationunit acquires signals at the same position. However, the opticalcoherence tomography device 1 may not scan measurement light at thecompletely coincident position if positioning of acquired signals issubsequently performed. For example, adjacent scanning positions may beset. In this way, the same position includes adjacent scanningpositions.

For example, the first image data generation unit may be configured togenerate first image data, which is image data representing phasedifference information in a plurality of OCT signals in the form of animage. First image data may be, for example, image data based on aDoppler OCT image (phase difference image) of Phase Difference, Phasevariance, Doppler variance, or the like.

The second image data generation unit may be configured to process theOCT signals to generate second image data, which is image datarepresenting information including the amplitude of the OCT signals inthe form of an image. Second image data may be, for example, image databased on a vector difference (VD) of the OCT signals. In this case, forexample, the second image data generation unit may process a pluralityof temporally different OCT signals with respect to the same position onthe specimen and may generate, as second image data, image datarepresenting the difference between a first vector based on phaseinformation and the amplitude information by a first OCT signal in theplurality of OCT signals and a second vector based on phase informationand the amplitude information by a second OCT signal in the form of animage.

Second image data may be, for example, image data which is acquired byprocessing various OCT signals from Scattering OCT, PolarizationSensitive OCT, Stereoscopic OCT, or the like.

The analysis processing unit may be configured to generate motioncontrast data based on the phase difference information in first imagedata generated by the first image data generation unit and informationincluding the amplitude in second image data generated by the secondimage data generation unit.

Accordingly, it may be possible to acquire image data with high contrastand less unnecessary signals (artifact) compared to individual imagedata of first image data and second image data.

When generating motion contrast data based on first image data andsecond image data, the analysis processing unit uses variouscombinations of image data for first image data and second image data.For example, image data based on a Doppler OCT image (phase differenceimage) may be used as first image data, and a vector difference (VD) ofan OCT signal may be used as second image data. For example, image databased on a Doppler OCT image (phase difference image) may be used asfirst image data, and image data obtained by processing an OCT signalacquired from Polarization Sensitive OCT or the like may be used assecond image data.

When processing a plurality of OCT signals to generate motion contrastdata, for example, the analysis processing unit may compute each set offirst image data and second image data to create motion contrast data.For example, when one of first image data and second image data is onepiece of image data obtained by processing a plurality of OCT signals,one piece of image data and the other piece computed for each set may becomputed to generated motion contrast data. For example, both firstimage data and second image data may be respective pieces of image dataobtained by processing a plurality of OCT signals, and two pieces ofimage data may be computed to generate motion contrast data.

The analysis processing unit may apply, to one piece of image data offirst image data and second image data, a filter using the other pieceof image data of the first image data and second image data to generatemotion contrast data. Applying the filter is regarded as weighting theother piece of data to one piece of data. For example, first image dataand second image data may be multiplied. For example, one piece of datamay be binarized into “1” and “0” based on a threshold value, and may bemultiplied by the other piece of data. Hereinafter, a kind of suchfilter processing is referred to as mask processing.

By performing the filter processing thus described, it may be possibleto compensate for the disadvantages of both pieces of data with theadvantages thereof and to acquire a satisfactory image.

The analysis processing unit may compute the phase differenceinformation in first image data generated by the first image datageneration unit and information including the amplitude in second imagedata generated by the second image data generation unit to obtainluminance with respect to each image of motion contrast data. Forexample, computation may be various types of computation, such asmultiplication, division, addition, subtraction, and integration aftermultiplication or logarithm.

A program which causes the optical coherence tomography device 1 toexecute the above-described processing may be stored in a storagemedium. In this case, a processor (for example, the control unit 70) maycause the optical coherence tomography device 1 to execute the programstored in the storage medium.

EXAMPLE

Hereinafter, one typical example according to the illustrativeembodiment will be described referring to the drawings. FIG. 1 is ablock diagram illustrating the configuration of an optical coherencetomography device 1 according to this example.

The optical coherence tomography device (hereinafter, abbreviated as anOCT device) 1 processes a detection signal acquired by the OCT opticalsystem 100. As an example, the OCT device according to the example isdescribed as a fundus imaging device which acquires a tomographic imageof a fundus oculi of a subject's eye.

Hereinafter, a configuration according to the example will be describedreferring to the drawings. FIG. 1 is a diagram showing the schematicconfiguration of the OCT device 1 according to this example. The OCToptical system 100 images a tomographic image from a fundus oculi Ef ofa subject's eye E. The device may include an en-face observation opticalsystem 200 and a fixation target projection unit 300. The OCT device 1is connected to the control unit 70.

The OCT optical system 100 irradiates the fundus oculi with measurementlight. The OCT optical system 100 detects an interference state ofmeasurement light reflected from the fundus oculi and reference light bya light receiving element (detector 120). The OCT optical system 100includes an irradiation position change unit (for example, an opticalscanner 108 and a fixation target projection unit 300) which changes anirradiation position of measurement light on the fundus oculi Ef so asto change an imaging position on the fundus oculi Ef. The control unit70 controls the operation of the irradiation position change unit basedon the set imaging position information and acquires a tomographic imagebased on a light reception signal from the detector 120.

<OCT Optical System>

The OCT optical system 100 has the device configuration of a so-calledoptical tomography interferometer (OCT: Optical coherence tomography)for ophthalmology, and images the tomographic image of the eye E. TheOCT optical system 100 splits light emitted from a measurement lightsource 102 into measurement light (sample light) and reference light bya coupler (light splitter) 104. The OCT optical system 100 guidesmeasurement light to the fundus oculi Ef of the eye E by a measurementoptical system 106 and guides reference light to a reference opticalsystem 110. Thereafter, interference light by synthesis of measurementlight reflected by the fundus oculi Ef and reference light is receivedby the detector (light receiving element) 120.

The detector 120 detects an interference signal of measurement light andreference light. In case of Fourier domain OCT, spectral intensity(spectral interference signal) of interference light is detected by thedetector 120, and a complex OCT signal is acquired by Fourier transformof spectral intensity data. For example, the absolute value of theamplitude in the complex OCT signal is calculated to acquire a depthprofile (A scan signal) in a predetermined range. The depth profile ateach scanning position of measurement light scanned by the opticalscanner 108 is arranged to acquire OCT image data (tomographic imagedata). Measurement light may be scanned in a two-dimensional manner toacquire OCT three-dimensional image data. An OCT en-face image (forexample, an integrated image integrated with respect to a depthdirection) may be acquired from OCT three-dimensional data.

A functional OCT signal may be acquired by analysis processing of thecomplex OCT signal. The functional OCT signal at each scanning positionof measurement light scanned by the optical scanner 108 is arranged toacquire functional OCT image data. Measurement light may be scanned in atwo-dimensional manner to acquire three-dimensional functional OCT imagedata. An OCT functional en-face image (for example, a Doppler en-faceimage or a signal image data spectral variance en-face image) may beacquired from three-dimensional functional OCT image data. The detailswill be described below.

For example, Spectral-domain OCT (SD-OCT) or Swept-source OCT (SS-OCT)may be exemplified. Time-domain OCT (TD-OCT) may be used.

In case of SD-OCT, a low-coherent light source (wideband light source)is used as the light source 102, and the detector 120 is provided with aspectral optical system (spectrometer) which spectrally separatesinterference light into respective frequency components (respectivewavelength components). The spectrometer has, for example, a diffractiongrating and a line sensor.

In case of SS-OCT, a wavelength scanning light source (wavelengthvariable light source) which temporally changes an emission wavelengthat high speed is used as the light source 102, and, for example, asingle light receiving element is provided as the detector 120. Thelight source 102 has, for example, a light source, a fiber ringresonator, and a wavelength selection filter. For example, a combinationof a diffraction grating and a polygon mirror or a filter using aFabry-Perot etalon is exemplified as the wavelength selection filter.

Light emitted from the light source 102 is divided into a measurementlight beam and a reference light beam by the coupler 104. Themeasurement light beam passes through an optical fiber and is thenemitted to the air. The light beam is condensed on the fundus oculi Efthrough other optical members of the optical scanner 108 and themeasurement optical system 106. Light reflected by the fundus oculi Efis returned to the optical fiber through the same optical path.

The optical scanner 108 scans measurement light on the fundus oculi in atwo-dimensional manner (in the XY direction (transverse direction)). Theoptical scanner 108 is disposed at a position substantially conjugate toa pupil. The optical scanner 108 is, for example, two galvanomirrors,and the reflection angle thereof is arbitrarily adjusted by a drivingmechanism 50.

Accordingly, a light beam emitted from the light source 102 is changedin the reflection (traveling) direction and is scanned in an arbitrarydirection on the fundus oculi. With this, the imaging position on thefundus oculi Ef is changed. As the optical scanner 108, a configurationin which light is polarized may be made. For example, other than areflection mirror (a galvanomirror, a polygon mirror, or a resonantscanner), an acoustic optical element (AOM) which changes the traveling(deflection) direction of light, or the like is used.

The reference optical system 110 generates reference light which issynthesized with reflected light acquired by reflection of themeasurement light on the fundus oculi Ef. The reference optical system110 may be of a Michelson type or a Mach-Zehnder type. For example, thereference optical system 110 is formed of a reflection optical system(for example, a reference mirror), reflects light from the coupler 104by the reflection optical system to return light to the coupler 104again, and guides light to the detector 120. As another example, thereference optical system 110 is formed of a transmission optical system(for example, an optical fiber), transmits light from the coupler 104without returning light, and guides light to the detector 120.

The reference optical system 110 has a configuration in which an opticalmember in a reference light path moves to change an optical path lengthdifference of measurement light and reference light. For example, thereference mirror moves in an optical axis direction. A configuration forchanging the optical path length difference may be disposed in themeasurement light path of the measurement optical system 106.

<En-Face Observation Optical System>

The en-face observation optical system 200 is provided so as to obtainan en-face image of the fundus oculi Ef. The observation optical system200 includes, for example, an optical scanner which scans measurementlight (for example, infrared light) emitted from the light source on thefundus oculi in a two-dimensional manner, and a second light receivingelement which receives fundus reflected light through a confocal openingdisposed at a position substantially conjugate to the fundus oculi, andhas a device configuration of a so-called scanning laser ophthalmoscope(SLO) for ophthalmology.

As the configuration of the observation optical system 200, a so-calledfundus camera type configuration may be used. The OCT optical system 100may be also used as the observation optical system 200. That is, theen-face image may be acquired using data which forms the tomographicimage obtained in a two-dimensional manner (for example, an integratedimage in a depth direction of a three-dimensional tomographic image, anintegrated value of spectrum data at each XY position, luminance data ateach XY position in a given depth direction, a retinal surface image, orthe like).

<Fixation Target Projection Unit>

The fixation target projection unit 300 has an optical system whichguides a visual line direction of the eye E. The projection unit 300 hasa fixation target which is presented to the eye E, and can guide the eyeE in a plurality of directions.

For example, the fixation target projection unit 300 has a visible lightsource which emits visible light, and changes a presentation position ofa visual target in a two-dimensional manner. With this, the visual linedirection is changed, and as a result, an imaging region is changed. Forexample, if the fixation target is presented from the same direction asthe imaging optical axis, the center part of the fundus oculi is set asan imaging region. If the fixation target is presented upward withrespect to the imaging optical axis, an upper part of the fundus oculiis set as an imaging region. That is, an imaging region is changedaccording to the position of the visual target with respect to theimaging optical axis.

As the fixation target projection unit 300, for example, a configurationin which a fixation position is adjusted by the turning-on positions ofLEDs arranged in a matrix, a configuration in which light from a lightsource is scanned using an optical scanner and a fixation position isadjusted by turning-on control of the light source, and the like areconsidered. The projection unit 300 may be of an internal fixation lamptype or an external fixation lamp type.

<Control Unit>

The control unit 70 includes a CPU (processor), a RAM, a ROM, and thelike. The CPU of the control unit 70 performs control of the entiredevice (OCT device 1, OCT optical system 100), for example, the membersof the configurations 100 to 300. The RAM temporarily stores varioustypes of information. The ROM of the control unit 70 stores variousprograms for controlling the operation of the entire device, initialvalues, and the like. The control unit 70 may be configured by aplurality of control units (that is, a plurality of processors).

A nonvolatile memory (storage unit) 72, a user interface (operationunit) 76, and a display unit (monitor) 75, and the like are electricallyconnected to the control unit 70. The nonvolatile memory (memory) 72 isa non-transitory storage medium which can hold the stored contents evenif power supply is shut off. For example, a hard disk drive, a flashROM, the OCT device 1, an USB memory which is detachably mounted in theOCT optical system 100, or the like can be used as the nonvolatilememory 72. The memory 72 stores an imaging control program forcontrolling imaging of an en-face image and a tomographic image by theOCT optical system 100. The memory 72 stores a fundus analysis programwhich allows the use of the OCT device 1. The memory 72 stores varioustypes of information regarding imaging, such as a tomographic image (OCTdata) in a scanning line, a three-dimensional tomographic image(three-dimensional OCT data), a fundus en-face image, and information ofan imaging position of a tomographic image. Various operationinstructions by an examiner are input to the user interface 76.

The user interface 76 outputs a signal according to an input operationinstruction to the control unit 70. As the user interface 74, forexample, at least one of a mouse, a joystick, a keyboard, a touch panel,and the like may be used.

A monitor 75 may be a display which is mounted in the device main body,or may be a display connected to the main body. A display of a personalcomputer (hereinafter, referred to as “PC”) may be used. A plurality ofdisplays may be used together. The monitor 75 may be a touch panel. Whenthe monitor 75 is a touch panel, the monitor 75 functions as an userinterface. Various images including a tomographic image and an en-faceimage imaged by the OCT optical system 100 are displayed on the monitor75.

<Operation of Device, Acquisition of Interference Signal>

In the optical coherence tomography device 1, a tomographic image isacquired. Hereinafter, an imaging operation of the device will bedescribed. The examiner instructs the subject to keep an eye on thefixation target of the fixation target projection unit 300 and thenperforms an alignment operation using the user interface 76 (forexample, a joystick (not shown)) while viewing an anterior eye partobservation image imaged by a camera for anterior eye part observation(not shown) on the monitor 75 such that a measurement optical axis is atthe center of the pupil of the subject's eye.

The control unit 70 acquires interference signals of at least twotemporally different frames at the same position. For example, thecontrol unit 70 controls the driving of the optical scanner 108 andscans measurement light on the fundus oculi. For example, measurementlight is scanned in the x direction along a first scanning line S1 shownin FIG. 3A. Scanning of measurement light in the x direction is referredto as “B-scan”. Hereinafter, an interference signal of one frame isdescribed as an interference signal obtained by single B-Scan. Thecontrol unit 70 acquires an interference signal detected by the detector120 during scanning. In FIG. 3A, the direction of a z axis is referredto as the direction of the optical axis of measurement light. Thedirection of the x axis is referred to as the direction perpendicular tothe z axis and right and left. The direction of the y axis is referredto as the direction perpendicular to the z axis and up and down.

When the first scanning is completed, the control unit 70 performssecond scanning at the same position as the first scanning. For example,the control unit 70 scans measurement light along the scanning line S1shown in FIG. 3A and scans measurement light again. The control unit 70acquires an interference signal detected by the detector 120 during thesecond scanning. Accordingly, the control unit 70 can acquireinterference signals of two temporally different frames at the sameposition. In this example, scanning at the same position is repeatedeight times, and interference signals of eight temporally differentcontinuous frames are acquired. For example, as shown in FIG. 3B,scanning in the scanning line S1 is repeated eight times, andinterference signals of eight frames are acquired.

When temporally different interference signals at the same position canbe acquired by single scanning, the second scanning may not beperformed. For example, when two beams of measurement light withdeviation in optical axis by a predetermined interval are scanned at onetime, it is not necessary to perform scanning multiple times. It shouldsuffice that temporally different interference signals at the sameposition in the subject can be acquired. When two beams of measurementlight are scanned at one time, it is possible to detect an arbitraryblood flow rate as an objective by the interval between two beams ofmeasurement light.

Similarly, the control unit 70 may acquire signals of at least twotemporally different frames at another position. As shown in FIG. 3A, afirst scanning line S1 is, for example, y=y1. A second scanning line S2is, for example, y=y2. If the acquisition of temporally differentsignals in the first scanning line S1 is completed, the control unit 70may successively signals of at least two temporally different frames inthe second scanning line S2.

The control unit 70 thus acquires signals at different times of thesubject. For example, in this example, scanning is repeated eight timesin the same line, and interference signals of eight frames are acquired.However, the number of frames is not limited to eight frames, and itshould suffice that interference signals of at least two temporallydifferent frames are acquired.

As shown in FIG. 3A, the control unit 70 raster-scans measurement lightand obtains interference signals of at least two temporally differentframes in each scanning line. Accordingly, it is possible to acquirethree-dimensional information inside a fundus oculi.

Raster scanning is a pattern in which measurement light is scanned on afundus oculi in a rectangular shape. Raster scanning is used as, forexample, OCT functional en-face image scanning.

In raster scanning, for example, measurement light is rasterized in ascanning region (for example, a rectangular region) set in advance. As aresult, a tomographic image in each scanning line is acquired inside thescanning region (for example, the rectangular region).

As scanning conditions in raster scanning, for example, a line width(the distance between a start point and an end point) in each of a mainscanning direction and a sub scanning direction, a scanning speed, theinterval between the scanning lines, the number of scanning lines, andthe like are set in advance. The scanning conditions in raster scanningmay be set arbitrarily.

In more detail, the control unit 70 scans measurement light in the mainscanning direction in a scanning line (first line) set as a startposition to functional OCT image data along the main scanning direction.Next, the control unit 70 scans measurement light in the main scanningdirection in a different scanning line with respect to the sub scanningdirection to form functional OCT image data along the main scanningdirection. As described above, functional OCT image data is obtainedwith respect to N different lines. Each scanning interval with respectto the sub scanning direction is narrowed, whereby functional OCT imagedata can be acquired in the scanning region. The scanning region isformed by different scanning lines with respect to the sub scanningdirection.

In the following description, an example where the sub scanningdirection is set as the y direction (up-down direction) and the mainscanning direction is set as the x direction (right-left direction) hasbeen described, the present disclosure is not limited thereto. Forexample, the sub scanning direction may be the x direction and the mainscanning direction may be the y direction.

In regards to scanning control in the sub scanning direction, a scanningposition may be changed in order from top to bottom or may be changed inorder from bottom to top. The scanning position may be changed in orderfrom the center to the periphery. As raster scanning, an interlacesystem may be used.

When acquiring temporally different interference signals at the sameposition, for example, the control unit 70 scans measurement light inthe main scanning direction multiple times in the first scanning lineS1. That is, after the first scanning from the start point to the endpoint ends in the first scanning line S1, the control unit 70 returnsthe scanning position of measurement light to the start point in thefirst scanning line S1 again and performs scanning in the first scanningline S1 again.

The control unit 70 generates functional OCT image data (for example,motion contrast data) corresponding to the first scanning line S1 basedon an output signal from the detector 120. Functional OCT image data isacquired by multiple scanning to the same scanning position. Forexample, the control unit 70 performs scanning the first scanning lineS1 until functional OCT image data of the number of frames set inadvance is obtained.

After multiple scanning in the first scanning line S1 ends, the controlunit 70 performs control such that the optical scanner 108 scansmeasurement light in the main scanning direction multiple times in thesecond scanning line S2. The control unit 70 generates functional OCTimage data corresponding to the second scanning line S2. For example,the control unit 70 performs scanning in the second scanning line S2until functional OCT image data of the number of frames set in advanceis obtained.

Similarly, the control unit 70 scans measurement light multiple times ineach scanning line up to the last scanning line Sn to generatefunctional OCT image data corresponding to each scanning line. That is,in the second scanning control, scanning is performed multiple times ineach scanning line.

The control unit 70 may perform control such that the OCT optical system100 acquires the interference signal and may perform control such thatthe observation optical system 200 acquires the fundus en-face image.

<Signal Processing Method>

A signal processing according to the example will be described referringto FIG. 4. The control unit 70 includes a processor (for example, a CPU)which controls various types of control processing, and a storage mediumwhich stores a program. The processor executes processing describedbelow according to the program. Processing of Steps 7 to 10 describedbelow is processing regarding a Doppler phase difference method.Processing of Steps 11 to 13 is processing regarding a vector differencemethod. In the following description, although a number for identifyingeach step of control is given, the given number does not necessarilymatch the number of actual control. In the following description, asignal at an n-th position (x,z) in an N frame is expressed by An (x,z).

(Step 1: Fourier Transform)

First, the control unit 70 performs Fourier transform of interferencesignal acquired by the OCT optical system. The control unit 70 obtains acomplex OCT signal An (x,z) by Fourier transform. The complex OCT signalAn (x,z) includes a real component and an imaginary component.

(Step 2: Image Registration)

In order to obtain a blood flow signal, it is necessary to comparetemporally different images at the same position. For this reason, it ispreferable that the control unit 70 performs positioning of images basedon image information (see FIGS. 5A and 5B). Image registration is aprocess in which a plurality of images in the same scene are arranged inalignment. As a factor for deviation in the position of the image, forexample, motion of the subject's eye during imaging is considered.

(Step 3: Phase Correction)

In Step 2, even if positioning between frames is performed, phasedeviation may occur between A-Lines in the same image (see FIG. 6).Accordingly, it is preferable to perform phase correction.

The control unit 70 repeatedly performs Steps 2 and 3 for each frame.The processing of Steps 2 and 3 is provided to easily perform theprocessing according to the example, and is not necessarily essential.

(Step 4: Generation of Intensity Image)

The control unit 70 acquires intensity information of the acquiredcomplex OCT signal. Signal intensity In (x,z) is expressed by Expression(1).I _(n)(x,z)=|A _(n)(x,z)|²  (1)

For example, the control unit 70 converts intensity information tobrightness to generate image data. For example, a region with largeintensity is expressed bright, and a region with small intensity isexpressed dark. In this way, in the description according to theexample, an image which expresses intensity information as informationof brightness is referred to as an intensity image.

(Step 5: Noise Reduction by Addition-Averaging Processing of IntensityImage)

The control unit 70 acquires a plurality (for example, eight) ofintensity images in Step 4. The control unit 70 adds and averages aplurality of intensity images using Expression (2). Accordingly,spectral noise or the like in each frame is reduced. For example, sincea signal based on measurement light reflected by a retinal layer isdetected with the substantially same value in a plurality of images,there is no significant change even after addition-averaging. Sincethere is a noise component randomly in eight images, the intensity ofthe noise component becomes small compared to a signal component.

$\begin{matrix}{{I_{n}\left( {x,z} \right)} = {\frac{1}{N}{\sum\limits_{n = 1}^{N}{I_{n}\left( {x,z} \right)}}}} & (2)\end{matrix}$

(Step 6: Segmentation)

The control unit 70 detects the boundary of each retinal layer from theimage subjected to addition-averaging and divides a cell region. Forexample, the cell region is classified into a nerve fiber layer (NFL), aganglion cell layer (GCL), a retinal pigment epithelium (RPE), and thelike.

(Step 7: Calculation of Phase Difference)

Next, the control unit 70 calculates the phase difference between OCTsignals A(x,z) acquired at two or more different times at the sameposition. For example, as shown in FIG. 7, a signal measured at the timeT1 is referred to as a signal A1, and a signal measured at the time T2is referred to as a signal A2. The control unit 70 calculates temporalchange in phase using Expression (3). In this example, for example,since measurement is performed at eight different times, calculation isperformed at T1 and T2, T2 and T3, T3 and T4, T4 and T5, T5 and T6, T6and T7, and T7 and T8 seven times in total, and seven pieces of data arecalculated. The symbol “*” in the expression represents a complexconjugate.Δϕ_(n)(x,z)=arg(A _(n+1)(x,z)×A _(n)*(x,z))  (3)

(Step 8: Removal of Part with Low S/N Ratio)

The control unit 70 removes a random phase difference in a region withlow signal-to-noise ratio (S/N ratio). For example, the control unit 70creates a histogram of intensity shown in FIG. 8 and searches for athreshold value at which a cumulative value becomes 75%. The controlunit 70 sets the values of a phase difference and a vector difference ofa region (a hatched region of FIG. 8) with intensity less than thethreshold value to 0. Accordingly, image noise is reduced.

(Step 9: Removal of Part with Small Phase Difference)

The control unit 70 removes a part with a small phase difference. Thisis to remove a reflection signal from a high reflection part, such as anerve fiber layer (NFL). Accordingly, it becomes easy to distinguishwhether a signal is a signal from a high reflection part or a signalfrom a blood vessel.

(Step 10: Denoising by Addition-Averaging Processing)

The control unit 70 adds and averages signals of seven frames subjectedto the above-described processing and removes noise. For example, thecontrol unit 70 performs addition-averaging processing using expression(4).

$\begin{matrix}{{{{\Delta\phi}\left( {x,z} \right)}} = {\frac{1}{N - 1}{\sum\limits_{n = 1}^{N - 1}{{{\Delta\phi}_{n}\left( {x,z} \right)}}}}} & (4)\end{matrix}$

(Step 11: Calculation of Vector Difference)

Subsequently, the vector difference will be described. The vectordifference of complex OCT signals detected by the OCT optical system iscalculated. For example, as in FIG. 9, a complex OCT signal can berepresented as a vector on a complex plane. Accordingly, signals A1 andA2 at the same position are detected at certain times T1 and T2, and avector difference ΔA is calculated by Expression (5), thereby generatingcontrast image data in the subject. When imaging the vector differenceΔA, for example, imaging may be performed based on phase information, inaddition to the magnitude of the difference ΔA.|ΔA _(n)(x,z)|=|A _(n+1)(x,z)−A _(n)(x,z)|  (5)

(Step 12: Removal of Low S/N Ratio Part)

Similarly to Step 8, a random phase difference component in a regionwith low S/N ratio is removed.

(Step 13: Addition-Averaging Processing)

The control unit 70 adds and averages signals for seven frames subjectedto the above-described processing and removes noise. For example, thecontrol unit 70 performs addition-averaging processing of the vectordifference using Expression (6).

$\begin{matrix}{{{\Delta\;{A\left( {x,z} \right)}}} = {\frac{1}{N - 1}{\sum\limits_{n = 1}^{N - 1}{{\Delta\;{A_{n}\left( {x,z} \right)}}}}}} & (6)\end{matrix}$

(Step 14: Multiply Images. Apply Filter)

The control unit 70 uses a calculation result of a phase difference as afilter to a calculation result of a vector difference. In thedescription according to the example, for example, “apply filter”performs weighting to a certain numerical value. For example, thecontrol unit 70 performs weighting by multiplying the calculation resultof the vector difference by the calculation result of the phasedifference. That is, a vector difference of a part with a small phasedifference is weakened, and a vector difference of a part with a largephase difference is strengthened. Accordingly, the calculation result ofthe vector difference is weighted to the calculation result of the phasedifference.

In the processing according to the example, the control unit 70multiplies the calculation result of the vector difference and thecalculation result of the phase difference. For example, the controlunit 70 multiplies the calculation result of the vector difference andthe calculation result of the phase difference using Expression (7).Accordingly, the control unit 70 generates a cross-section angiogram CAwhich is weighted by the calculation result of the phase difference.

The calculation result of the vector difference and the calculationresult of the phase difference are multiplied, whereby it is possible tocancel the disadvantages of the respective measurement methods and toskillfully detect an image of a vascular part.

For example, as described above, when the PD method is used, a bloodvessel and a background part are detected strongly. A high reflectionpart, such as an NFL, is detected weakly (see FIG. 10). This is becausethe blood vessel and the background part have large fluctuation inphase, and the high reflection part, such as an NFL, has smallfluctuation in phase.

When the VD method is used, a blood vessel is detected strongly, abackground part is detected weakly, a high reflection part, such as anNFL, is detected more weakly than the blood vessel and more stronglythan the background part (see FIG. 11). This is because the blood vesselhas fluctuation in amplitude and phase of an OCT signal; the backgroundpart has small fluctuation in amplitude and small fluctuation in phase;and the high reflection part, such as an NFL, has small fluctuation inphase and has large fluctuation in amplitude.

When two types of motion contrast are multiplied, since the vascularpart is detected strongly using any method, the vascular part isdetected strongly after multiplication. Since the background part isdetected strongly in the PD method, but is detected weakly in the VDmethod, the background part is detected weakly after multiplication.Since the high reflection part, such as NFL, is detected strongly to acertain degree in the VD method, but is detected weakly in the PDmethod, the high reflection part is detected weakly aftermultiplication. In this way, the calculation result of the PD method andthe calculation result of the VD method are multiplied, whereby only thevascular part is detected strongly. Two signals are multiplied, wherebyit is possible to remove an artifact which is detected in each of the PDmethod and the VD method (see FIG. 12).

The control unit 70 repeats Steps 1 to 14 for each scanning line andgenerates the cross-section angiogram CA for each scanning line.CA(x,z)=|Δϕ(x,z)|×|ΔA(x,z)|  (7)

(Step 15: Add in z Direction for Each Layer of Fundus Oculi to GenerateEn-Face Image.)

The control unit 70 integrates the cross-section angiogram CA obtainedfrom Expression (7) in the z direction for each layer of the fundusoculi divided by segmentation of Step 6 to generate an en-face angiogramEA. For example, when generating an integrated image from an innerlimiting membrane (ILM) of the fundus oculi to a visual cell innersegment-outer segment joint (IS/OS), Expression (8) is used.EA(x,y)=∫_(ILM) ^(IS/OS) CA(x,y,z)dz  (8)

The control unit 70 performs the above-described processing to generatean angiographic image shown in FIG. 13. The control unit 70 may displaythe generated image on the display unit. Data may be transferred toother devices.

In this example, functional OCT image data of the subject is thusacquired using at least two methods including the signal processingmethod using the phase difference and the signal processing method usingthe vector difference. Accordingly, it is possible to acquire a morevivid image by compensating for the advantages and disadvantages of therespective measurements.

For example, conventional fluorescein fluorescence fundus angiography(FA) and the like can only generate a fully integrated image. However,in the optical coherence tomography device 1 according to the example,it is possible to generate an image integrated in each retinal layer.Accordingly, it is possible to observe a blood vessel by retinal layer.The type of a blood vessel is different by retinal layer. For example,there are many blood vessels, called a surface capillary of a retina, ina nerve fiber layer, and there are many blood vessels, called a deepcapillary, in an inner granular layer. For this reason, it is preferableto observe an adequate retinal layer based on a diagnostic item.

It is possible to achieve three-dimensional visualization by volume dataof a vascular structure. In the method according to the example, sincean artifact or the like in the shadow of the blood vessel is reduced, itis possible to acquire a satisfactory three-dimensional image.

Modification Example of First Example

In Step 14, although the calculation result of the vector difference andthe calculation result of the phase difference are multiplied, thepresent disclosure is not limited thereto. For example, a mask based onthe calculation result of the phase difference may be used to the vectordifference. In this embodiment, “mask” is, for example, processing inwhich a value greater than a certain threshold value is used as it is,and a value smaller than a certain threshold value is set to “0”.Accordingly, when a mask based on the phase difference is used, forexample, the control unit 70 applies “0” to the calculation result ofthe vector difference in a region where the phase difference is equal toor less than 0.4 radian. The control unit 70 applies “1” to thecalculation result of the vector difference in a region where the phasedifference is equal to or greater than 0.4 radian.

In the mask generated based on the calculation result of the phasedifference, a high reflection part, such as an NFL or a RPE, with lesssignals becomes “0”. For this reason, the control unit 70 can set asignal of a high reflection part to be a problem in the VD method to 0,thereby decreasing signals of unnecessary parts other than a bloodvessel.

In the above description, although a PD filter or the like is used inthe VD method, the present disclosure is not limited thereto. Forexample, a PD filter or the like may be used to the result obtained forthe above-described spectral variance. A Doppler filter or the like maybe used to an addition average of intensity.

In the above description, although two signals (image data) aremultiplied, two or more signals may be multiplied. For example, threesignals may be multiplied. For example, a signal for DOPU (degree ofpolarization uniformity) or the like may be multiplied. The DOPU is avalue representing polarization uniformity. That is, the device maymultiply at least two of a plurality of pieces of functional OCT imagedata and image data to generate a new functional OCT image.

The control unit 70 may be configured to apply a filter, based on thecalculation result of the phase difference, onto the image data obtainedfrom the OCT signal, which may contain complex images and image databased on the vector difference. For example, the control unit 70 mayapply a filter on a pixel having smaller calculation result of the phasedifference to lessen signal intensity in the image data. The controlunit 70 may apply a filter on a pixel having larger calculation resultof the phase difference to enlarge signal intensity in the image data.The control unit 70 may be configured to adjust the correction ratio ofthe signal intensity according to the calculation result of the phasedifference, or may be configured to apply the same correction ratio ofthe signal intensity, when applying the filter.

Second Example

Hereinafter, a second example will be described for a part differentfrom the first example. In the first example, the control unit 70 usesthe result in the PD method as the filter or the like. In the secondexample, the control unit 70 uses a measurement result in the VD methodas a mask. For example, in the second example, the measurement result inthe VD method is used as a mask to a measurement result in the PDmethod.

Accordingly, in the second example, similarly to the first example, itis possible to acquire a more vivid image by compensating for theadvantages and disadvantages of the PD method and the VD method.

In a method of detecting a vector difference, information correlatedwith the blood flow rate is not obtained. However, a Doppler phase angleis correlated with speed. In a method which uses a VD mask to the resultof the PD method, information of a Doppler phase angle is left.Therefore, the control unit 70 can obtain the blood flow rate. If theblood flow rate can be obtained, it is possible to perform diagnosis ofvarious diseases.

What is claimed is:
 1. An optical coherence tomography devicecomprising: an OCT optical system configured to detect measurement lightirradiated onto a specimen and a reference light and output OCT signalbased on the measurement light and the reference light; and an analysisprocessing unit configured to process the OCT signal and generate motioncontrast data of the specimen, wherein the analysis processing unitcomprises: a first image data generation unit configured to generatefirst motion contrast image data by applying first analysis processingon the OCT signal; and a second image data generation unit configured togenerate second motion contrast image data by applying second analysisprocessing that is different from the first analysis processing on theOCT signal, and wherein the analysis processing unit applies the secondmotion contrast image data as a filter onto the first motion contrastimage data to remove an artifact at a high reflection portion.
 2. Theoptical coherence tomography device according to claim 1, wherein theanalysis processing unit applies to the first motion contrast image dataa weight based on the second motion contrast image data.
 3. The opticalcoherence tomography device according to claim 1, wherein the highreflection portion is a nerve fiber layer (NFL).
 4. The opticalcoherence tomography device according to claim 1, wherein the firstimage data generation unit generates a Doppler OCT image as the firstmotion contrast image data.
 5. The optical coherence tomography deviceaccording to claim 1, wherein the second image data generation unitprocesses the multiple OCT signals which is a plurality of OCT signalsoutput from the OCT optical system being obtained at a different timingfor the same position on the specimen and generates, as the secondmotion contrast image data, image data representing difference between afirst vector based on phase information and the amplitude information ofa first OCT signal selected from the multiple OCT signals and a secondvector based on phase information and the amplitude information of asecond OCT signal selected from the multiple OCT signals.
 6. The opticalcoherence tomography device according to claim 1, wherein the analysisprocessing unit applies, to one of the first motion contrast image dataand the second motion contrast image data a filter based on another oneof the first motion contrast image data and the second motion contrastimage data.
 7. The optical coherence tomography device according toclaim 1, wherein the analysis processing unit applies, to one of thefirst motion contrast image data and the second motion contrast imagedata a mask based on another one of the first motion contrast image dataand the second motion contrast image data.
 8. The optical coherencetomography device according to claim 1, wherein the analysis processingunit obtains luminance with respect to each pixel of the motion contrastdata by computing the phase difference information in the first motioncontrast image data generated by the first image data generation unitand the amplitude information in the second motion contrast image datagenerated by the second image data generation unit.
 9. The opticalcoherence tomography device according to claim 8, wherein the analysisprocessing unit obtains the luminance with respect to each pixel of themotion contrast data by multiplying the phase difference information inthe first motion contrast image data generated by the first image datageneration unit and the amplitude information in the second motioncontrast image data generated by the second image data generation unit.10. The optical coherence tomography device according to claim 1,wherein at least one of the multiple OCT signals is utilized as the OCTsignal from which the second image data generation unit generates thesecond motion contrast image data.
 11. The optical coherence tomographydevice according to claim 1 further comprising: a control unitconfigured to control the OCT optical system to output at least twoframes of OCT signals being obtained at a different timing for the sameposition on the specimen as the multiple OCT signals from which thefirst motion contrast image data is generated by the first image datageneration unit.
 12. The optical coherence tomography device accordingto claim 1 further comprising: a control unit configured to control theOCT optical system to output at least two frames of OCT signals beingobtained at a different timing for the same position on the specimen asthe OCT signal from which the second motion contrast image data isgenerated by the second image data generation unit.
 13. The opticalcoherence tomography device according to claim 1, wherein the secondimage data generation unit generates the second motion contrast imagedata by processing the multiple OCT signals which is a plurality of OCTsignals output from the OCT optical system being obtained at a differenttiming for the same position on the specimen.
 14. The optical coherencetomography device according to claim 13, wherein the first image datageneration unit and the second image data generation unit generate thefirst motion contrast image data and the second motion contrast imagedata from the same set of the OCT signals.
 15. The optical coherencetomography device according to claim 13, wherein the first image datageneration unit generates the first motion contrast image data as aDoppler OCT image being obtained from a phase difference of the multipleOCT signals, and wherein the second image data generation unit generatesthe second motion contrast image data as a vector difference imageobtained from a vector difference of the multiple OCT signals.